Chlorinated polyvinyl chloride (CPVC) offers advantages over polyvinyl chloride. For example, chlorinated polyvinyl chloride can withstand water at temperatures greater than 60° C. to 70° C. or higher, which is an advantage over polyvinyl chloride, and thus makes chlorinated polyvinyl chloride suitable for use as a material for water piping systems in residential and commercial construction. Chlorinated polyvinyl chloride also has greater resistance to many chemicals.
Chlorination of polyvinyl chloride resin to produce chlorinated polyvinyl chloride is generally known in the art. Chlorinated polyvinyl chloride can be made via a free radical chlorination reaction of polyvinyl chloride particles. The reaction can occur via a radically initiated reaction wherein a chlorine radical adds to the polyvinyl chloride. For example, chlorine gas can be decomposed into free radical chlorine by UV light, and the radical chlorine is then reacted with polyvinyl chloride resin, essentially replacing a portion of the hydrogen in the polyvinyl chloride molecule with chlorine.
There have been prior art efforts directed to improving the synthesis of chlorinated polyvinyl chloride. For example, U.S. Pat. No. 2,996,489 discloses the use of a swelling or wetting agent, such as a chlorinated hydrocarbon to improve diffusion of the chlorine through the polyvinyl chloride polymer particle. Similarly, U.S. Pat. No. 3,334,077 discloses a method of chlorinating polyvinyl chloride resin in an aqueous medium containing an organic swelling agent for the polyvinyl chloride resin, where the chlorination reaction is conducted in the presence of an acrylic acid polymer.
The prior art has further recognized the problem of relatively slow chlorination rates of vinyl chloride resins. For example, U.S. Pat. No. 3,100,762 describes obtaining faster chlorination than proposed in U.S. Pat. No. 2,996,489 by conducting the chlorination at elevated temperature and pressure in the presence of a swelling agent, and in the absence of photo-illumination. It is suggested that neither catalyst nor photo-illumination is required under the prescribed conditions of temperature and pressure if oxygen is substantially excluded from the reactor. Significantly, however, inferior chlorinated products are obtained under these reaction conditions when the chloromethane swelling agent is omitted from the reaction mixture.
In a further effort to improve chlorination rates, U.S. Pat. No. 4,412,898 discloses photo-chlorination of polyvinyl chloride particles in an aqueous suspension without the use of swelling agents by employing elevated pressure and temperature.
Despite improvements that have been made, there remains a desire to improve the chlorination rate of PVC.